1. Field of the Invention
The present invention relates to an automatic transmission controller.
2. Description of Related Art
A known automatic transmission controller controls an automatic transmission by supplying a fluid pressure to a friction element of the automatic transmission. This kind of automatic transmission controller, described in JP-A-H05-296327, applies a standby pressure (a low fluid pressure at which the friction element is not engaged) to the friction element that is in a disengaged state to obtain a high engagement response.
The automatic transmission controller described in JP-A-H05-296327 applies an output pressure of an electromagnetic valve directly to the friction element. In such a case, the output pressure of the electromagnetic valve supplied to the friction element acutely responds to a resistance change of a coil inside the electromagnetic valve that depends on an ambient temperature change.
Generally, an engaging pressure for engaging the friction element in a forward range or in a reverse range is set low. Therefore, the standby pressure of the friction element should be lower than that. At low temperatures, at which fluidity of the fluid is low, it is difficult to accurately regulate the extremely low standby pressure with the electromagnetic valve. Accordingly, there is a possibility that the friction element may be engaged unexpectedly.